Electron Impact Mass Spectra With Supercritical Fluid Chromatography/Mass Spectrometry

An SFC/MS system has been constructed through additions and appropriate modifications to a GC/MS instrument. Supercritical fluid conditions were effected by transport of liquid carbon dioxide mobile phase through a micro pump to the injector and then into a fused silica capillary column. Two approaches to a successful coupling of the resultant effluent to the GC/MS system in order to yield EI mass spectra have been demonstrated. In one configuration, an open-split GC/MS interface was used to eliminate excess mobile phase. Inside the heated interface was a frit restrictor connected to a deactivated, uncoated fused silica capillary column (also heated) which functioned as a transfer line into the ion source. An alternate configuration omitted the open-split interface and located the frit restrictor inside the ion source. A specially fabricated stainless steel rod, heated by the ion source heater, had a conical opening into which the restrictor tip was positioned and also heated. In both configurations, a turbomolecular pump was used in the ion source. In the above systems, EI mass spectra were satisfactorily produced without ion-molecule contributions or carbon dioxide clusters. The resulting spectra can thus be searched against a conventional mass spectral library for the identification of compounds separated by supercritical fluid chromatography.